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First test with the new telescope

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#1 TareqPhoto

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Posted 04 June 2020 - 04:22 AM

First test ever with my new scope, GSO 6" F/4, the collimation is not perfect, and the balance is also not good, no polar alignment as i was in hurry, but i wanted to see if the mirrors are not good or just normal quality acceptable anyway.

 

Also it is a test for my latest camera, ASI178MC, not sure if those are good examples to judge, but i feel/think that the scope is good enough, the more care and better collimation i can do the better results i can get, so i will be patient with it.

 

First one is RAW16 mode without filter, second also no filter at RAW8, the last two are with Baader Neodymium Moon&Skyglow filter, third is at RAW8 and last is RGB42 mode.

 

 

21-43-24-RAW16.jpg

 

21-45-34-RAW8.jpg

 

21-55-13-Baader-Neodymium-RAW8.jpg

 

21-59-05-Baader-Neodymium-RGB24.jpg


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#2 BQ Octantis

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Posted 04 June 2020 - 04:37 AM

Looks pretty colorful to me!

 

Were you happy with the results?

 

BQ



#3 TareqPhoto

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Posted 04 June 2020 - 04:44 AM

Looks pretty colorful to me!

 

Were you happy with the results?

 

BQ

Not completely, but the results telling me that the scope isn't bad at all, i can't judge it from one test one night and without perfect or almost precise collimation to give final judgement, i bought it more for DSO, but the moon is my favorite target always for test and practice.

 

You tell me, if you got those results, would you be happy with them? What will you change or do differently?

 

Tareq



#4 BQ Octantis

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Posted 04 June 2020 - 04:56 AM

I hate the moon. So I'd first change the target! lol.gif

 

In all seriousness, the images seem quite sharp on the left and a little soft on the right. Not sure if this is collimation or something else. Reco a long-ish exposure on a bright star field—the edge coma on the stars on the periphery will point the way to the collimation point.

 

BQ


Edited by BQ Octantis, 04 June 2020 - 04:57 AM.

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#5 TareqPhoto

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Posted 04 June 2020 - 05:07 AM

I hate the moon. So I'd first change the target! lol.gif

 

In all seriousness, the images seem quite sharp on the left and a little soft on the right. Not sure if this is collimation or something else. Reco a long-ish exposure on a bright star field—the edge coma on the stars on the periphery will point the way to the collimation point.

 

BQ

Someone pointed me that it is the coma, i may try to use a coma corrector one day and give it a try for planetary, but i already did that with the mono cooled camera as i placed coma corrector to image DSO, but i gave the moon a quick last tests with the mono cooled before i slew to a DSO target, the camera was with CC, but the view of the moon is small and almost in the center of the FoV, so it is not a good confirmation too, tilt isn't a cause here, so either collimation or coma.

 

Well, if you come here then the moon will be your first or second favorite target, i believe you didn't see the moon good or clear enough wink.gif grin.gif



#6 BQ Octantis

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Posted 04 June 2020 - 05:23 AM

With edge coma (like the massive, uncorrectable coma I get from my C5/750), you want to make sure you place your DSO or planet at the center of collimation. From your moon image, this is not at the center of the sensor; it's somewhere on the left side.

 

BQ



#7 TareqPhoto

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Posted 04 June 2020 - 05:29 AM

With edge coma (like the massive, uncorrectable coma I get from my C5/750), you want to make sure you place your DSO or planet at the center of collimation. From your moon image, this is not at the center of the sensor; it's somewhere on the left side.

 

BQ

The problem is with cameras like planetary ones it will be so tight FoV, so definitely the moon will be touching edges, either one edge or both, even if i center it, but i think you are right, i might shifted the moon to one edge more, and you said left so there is more noticeable coma effect, i can always try again, i just want to use this scope for DSO more and more, the first test of DSO was bad, but i learn from that.



#8 Tom Glenn

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Posted 04 June 2020 - 05:52 AM

Even if your collimation is perfect, an f/4 Newtonian will not cover the ASI178 sensor without coma, unless you use a coma corrector.  The diameter of the coma free field of a scope (in mm) is approximately given by the formula 0.022*f^3, in which f is the focal ratio.  So for an f/4 scope, this gives a value of 1.4mm across.  The ASI178 sensor is much larger than this, at 5mm x 7.4mm.  So you will definitely need a coma corrector.  The blurring on the right side of your image looks like coma to me, and also indicates that the scope is not collimated on the centerline of the sensor.  



#9 TareqPhoto

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Posted 04 June 2020 - 06:09 AM

Even if your collimation is perfect, an f/4 Newtonian will not cover the ASI178 sensor without coma, unless you use a coma corrector.  The diameter of the coma free field of a scope (in mm) is approximately given by the formula 0.022*f^3, in which f is the focal ratio.  So for an f/4 scope, this gives a value of 1.4mm across.  The ASI178 sensor is much larger than this, at 5mm x 7.4mm.  So you will definitely need a coma corrector.  The blurring on the right side of your image looks like coma to me, and also indicates that the scope is not collimated on the centerline of the sensor.  

I see, so all my cameras either planetary or DSO it will be all not good covering the coma then, new thing to learn, so i will try next time to use coma corrector with the Newt either this 6" or even 8" F5, but what about if i try to use Powermate 2x or even 5x with this scope, how can i correct coma if using a focal extender? 



#10 happylimpet

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Posted 04 June 2020 - 06:33 AM

Youve gotta be really careful about positioning your target at f4. Even at f5 with perfect collimation, the edges of my planetary cameras (224mc or 290mm) display coma. (this is imaging at f20 with a barlow , to be clear)

 

So I always make a point of finding the sweet spot before imaging. And then the ADC throws the sweet spot right out of the FOV...grrr...



#11 TareqPhoto

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Posted 04 June 2020 - 06:51 AM

Youve gotta be really careful about positioning your target at f4. Even at f5 with perfect collimation, the edges of my planetary cameras (224mc or 290mm) display coma. (this is imaging at f20 with a barlow , to be clear)

 

So I always make a point of finding the sweet spot before imaging. And then the ADC throws the sweet spot right out of the FOV...grrr...

Just tell me and make it very clear and simple, if i will image planetary with Newtonian be it F2 or F200, do i need coma corrector always? Do i need to use coma corrector with Barlow or Powermate as well? Does using ADC neglecting coma? I mean should i use coma corrector no matter what other tools i will use as long it is a Newt not corrected? 




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